1. Field of the Invention
The present invention relates generally to a medical particle irradiation apparatus, and more particularly to a medical particle irradiation apparatus which is suitable for rotating around the patient and irradiating the patient with particle beams from a desired location in the circumferential direction.
2. Description of the Related Art
Particle beams (e.g., proton beam) have captured the spotlight in recent years in radiation therapy (treatment) for cancer as they can treat cancer with relatively small damage to normal cells.
An example of rotary irradiation room for radiation therapy using particle beams is described in Patent Document 1. This rotary irradiation room for radiation therapy has a semicylindrical path with a level bottom formed at each of the fixed and mobile ring rails which are provided opposite each other with the radiation irradiation unit between them, and the flexible moving floor provided within this path is moved in synchronization with the rotation of the radiation irradiation unit. Further, the drive motor provided on the rotating gantry rotates the mobile ring rail in the direction opposite to the radiation irradiation unit""s rotation direction by the same amount as the amount of rotation of the radiation irradiation unit. This keeps the positional relationship between the fixed and mobile ring rails which are located opposite each other and allows consistent formation of a level floor used for access to the therapy bed and the radiation irradiation unit even when the rotating gantry rotates.
However, this prior art requires a drive motor for rotating the mobile ring rail in the direction opposite to the rotating gantry""s rotation direction and a tilt sensor for detecting the relative positional relationship between the semicylindrical passages formed at the fixed and mobile ring rails and moreover a control unit for controlling them, thus making the configuration complex.
Therefore, an example of rotary irradiation room for particle beam therapy addressing this problem is described in Patent Document 2. This rotary irradiation room for particle beam therapy comprises a fixed shell and fixed shell-side guide rail and rotary shell-side guide rail and activates the locking rod using motor-operated cylinders provided on the fixed shell; this locking rod is engaged with an engagement holes provided on the rotary shell-side guide rail during rotation of the rotating gantry. For this reason, the rotation of the rotary shell-side guide rail is inhibited by the locking rod during rotation of the rotating gantry, thus making it possible to keep the positional relationship between the fixed and rotary shell-side guide rails which are located opposite to each other and keep the bottom of the moving floor constantly level. Two motor-operated cylinders and two engagement holes are provided; the locking rod is pulled out of the engagement hole and reduced in size on the side where the rotation of the particle irradiation unit is hindered while the locking rod is kept in the engagement hole on the side where the rotation is not hindered.
[Patent Document 1]
Japanese Patent Application Laid-open (kokai) Publication No. Hei11-47287
[Patent Document 2]
Japanese Patent Application Laid-open (kokai) Publication No. 2001-129103
Although the drive motor and the tilt sensor in the prior art described in Patent Document 1 are not needed, the prior art described in Patent Document 2 additionally requires locking rods, motor-operated cylinders and a control unit for causing the locking rod to extend or retract with rotation of the particle irradiation unit and attaching and detaching the locking rod, thus resulting in insufficient simplification of the configurations.
It is therefore the object of the present invention to provide a medical particle irradiation apparatus which ensures more simplified structure and allows formation of the substantially level access floor regardless of the position of the irradiation unit which emits particle beams.
The above object can be achieved by providing an anti-corotation unit which is in contact with both a first frame located within and supported by a rotating gantry such that it can rotate relative to the rotating gantry and a second frame fixedly located opposite the first frame and which prevents the first frame from rotating together with the rotating gantry during rotation of the rotating gantry. Further, the flexible moving floor, interposed between the first and second frames, is engaged with the first and second frames in such a manner as to move freely such that its bottom is substantially level, that it forms therein a particle irradiation room into which a therapy bed is slid and that it moves as the rotating gantry rotates.
Since the anti-corotation unit is in contact with the first frame, located within the rotating gantry such that it can rotate relative to the rotating gantry, and the fixed second frame, the anti-corotation unit which is in contact with the second frame can prevent rotation of the first frame even if the first frame attempts to rotate together with the rotating gantry during rotation of the rotating gantry. Therefore, the positions of the first and second frames which are located opposite each other can be kept substantially unchanged even if the rotating gantry rotates. Consequently, it is possible for the flexible moving floor to form a substantially level access floor regardless of the position of the irradiation unit emitting particle beams.
Moreover, since the anti-corotation unit is located on the rotating gantry, it is moved in the rotating gantry""s rotation direction as a result of rotation of the rotating gantry. However, the present invention eliminates the need for the drive motor described in Patent Document 1 which rotates the mobile ring rail in the direction opposite to the rotation direction of the radiation irradiation unit by the same amount as the amount of rotation of the radiation irradiation unit and the drive unit exclusively for the anti-corotation unit, an equivalent of the motor-operated cylinder described in Patent Document 2 which moves the locking rod. The present invention does not require any exclusive drive unit for the anti-corotation unit and any control unit for this drive unit, thus allowing simplification of the structure.
It is also possible to dispose the anti-corotation unit on the irradiation unit which rotates together with the rotating gantry during rotation of the rotating gantry and emits particle beams. Disposition of the anti-corotation unit on the irradiation unit means that the anti-corotation unit lies on the rotating gantry although it is not directly disposed on the rotating gantry.